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Full text of "Handbook Of Chemical Engineering - I"

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BY F. F.
Introduction. — In industrial establishments the means of elevating and transporting liquids may be roughly classified into piston pumps and pistonless pumps, the latter including pulsometers, jet pumps, air lifts, eggs or montejus, centrifugal pumps and rotary pumps.
Single direct-acting pumps have one steam (or air) cylinder and one pump body, both double-acting. The essential part of the valve motion is a pilot valve controlling a valve piston which mechanically operates the main steam valve. The main ports terminate a short distance from the end of the cylinder and a small port relieves the compression and admits steam behind the piston for starting, see Fig. 1. Advantages over duplex pumps are: greater simplicity, as only two stuffing boxes and one pump piston have to be cared for; also somewhat higher economy because the piston must make a full stroke before it throws the pilot valve. This is of especial advantage in wet vacuum pumps, as it
FIG. 1.—Laidlaw-Dunn-Gordon horizontal valve motion.
reduces the clearance. A disadvantage is the intermittent action of the plunger, resulting in shocks in the pipes, which must be taken up by large air chambers. These shocks are especially violent at higher speeds and when the liquid carries much entrained gas. Plunger and ring pumps should be used for clean water only, as grit and dirt rapidly destroy the fit and cause leakage.
Simple cylinder direct-acting duplex pumps are widely used for all purposes. Figure 2 shows a standard design. It consists of two steam cylinders and two water ends, arranged side by side. Each steam piston is directly connected to its
1 Consulting engineer, 421 Hillside Place, South Orange, N. J.